Linear gas-burner with adjustable width

ABSTRACT

This burner comprises a gas distributor (20) with a row of gas injectors (5a to 5e), the tube being axially inside an air distributor tube. Each gas injector extends through the wall of the air distributor tube via a coaxial air outlet aperture. The gas distributor tube includes two sealing bodies (36, 37) sliding symmetrically on either side of a central gas inlet aperture (21). Each of these bodies is provided with an eccentric longitudinal threaded bore (38, 39) engaging a threaded section of a rotating control rod (41). The two sections (48, 49) are threaded in opposite directions to the thread of the sealing bodies (36, 37), which enables them to move these two sealing bodies simultaneously in order to gradually interrupt or restore the supply of gas to the injectors (5a to 5e) situated at the end of the row without interrupting the supply to the air injectors.

The present invention concerns a linear gas and blown air burner,comprising an air distributor tube connected to a pressurized airsupply, a gas distributor tube fitted inside the air distributor tubeand equipped with a gas inlet connected to a pressurized gas supply, andat least one longitudinal row of gas injectors, these injectorsextending virtually radially from the gas distributor tube through airinjectors fitted on air outlet apertures made in the wall of the airdistributor tube, each gas injector being fitted on a gas outletaperture made in the wall of the gas distributor tube.

BACKGROUND OF THE INVENTION

Such a linear gas burner, described in the European patent No. 0190091,offers great advantages from a security point of view, as the mixing ofthe gas with the blown air occurs only at the inlet of the combustionzone, and from a convenience point of view as it has a very high ratiobetween its maximum power and its minimum power. This is why it is verywidely used, notably in the food industry and in the textile industry.This is the case in particular with textile finishing machines,especially drying and heatsetting tenters where it permits both anoptimal distribution of the heat over the whole surface of the productto be treated and a modulation of power of up to 1:50 which, in uses asdifferent as the drying of the fabrics or the heatsetting of the dyes,permits treatment at very precise temperatures whatever the heatrequirement. In this perspective, such linear gas burners are startingto be used in place of steam, of electricity or of thermofluid heating,to inwardly heat drying drums formed by a rotating metallic casing overwhich passes a band of a product to be dried such as a fabric, a sheetof paper, etc. Firstly, gas is, at present, a cheap form of energy,which can be used with a very high output and secondly, it enableshigher temperatures to be obtained than with steam heating, which isnecessary in certain heat treatments. Moreover, more precise and moreevenly distributed temperatures are obtained, notably compared withthermofluid or electric heating. Finally, a gas-burner is a heatingdevice which can be used independantly without being linked to otherinstallations, and in particular to a boiler room. Moreover, comparedwith other types of linear gas-burners such as pre-mixing burners, theuse of a burner of the type indicated above is particularly worthwhiledue to its great possibility of power modulation, which allows a veryprecise adjustment.

However, the need exists to be able to adjust in quite a precise way,the width of the zone to be heated. For example, in a fabric dryingdrum, trials have shown that the evenness of the drying is closelylinked to the active width of the gas-burner. If the fabric is of agreater width than the burner, its selvages will be insufficientlydried. If the burner has an active width greater than that of thefabric, the latter will be excessively dried near its selvages. Indeed,the zones at the extremities of the drum, which are not covered by thefabric but are nonetheless heated by the burner, can reach an excessivetemperature of up to around 400° C. which is detrimental both for thedrum and the fabric. If burners which pre-mix the gas and the combustionair are used, it is not too difficult to conceive a mechanism whichreduces the active length of the burner, by progressively sealing thegas outlet apertures. Publication GB-A-204 756 shows a linear pre-mixedgas burner which has a distributor tube supplied half way along itslength and sealed by two pistons fitted on an axial shaft threaded intwo opposite directions. However, this type of pre-mixing burner belongsto a technology which is fundamentally different from that of pure gasburners and has other drawbacks mentioned above. In a pure gas and blownair burner of this type, one solution could consist in dividing theburner up into several linear or punctual burners, with outside valveson the corresponding gas supplies. However, such a solution iscomplicated, bulky and costly, and it only allows a relatively roughadjustment thread.

SUMMARY OF THE INVENTION

The present invention thus aims at providing a linear gas-burner of thetype indicated in the preamble, equipped with a device enabling theactive width of the flame to be precisely adjusted, by maintainingeither engaged or not, individually, at least the injectors situatednear an extremity of the row.

With this aim, the burner according to the invention is characterized inthat the gas distributor tube is inwardly sealed by at least one slidingsealing body fitted so as to block the gas supply of a section of thistube comprising one or several gas injectors, the said sealing bodybeing coupled with a control rod set out longitudinally in this tube andlinked to means of control situated outside this tube, and in that allthe air injectors of the said row continue to be supplied with air whenthe gas supply of one or several gas injectors is blocked by the saidsealing body.

In a preferred embodiment, the control rod is rotary around its axle andcomprises at least one threaded section which is fitted into acorresponding threaded bore of the sealing body, and the sealing body isequipped with means which prevent it from turning in the gas distributortube. The control rod can be fitted in a rotary way in two elementsclosing the extremities of the gas distributor tube, the rod goingthrough at least one of the elements to be linked to the means ofcontrol.

Preferably, the gas distributor tube has a circular cross section, ashas the sealing body, and to prevent the sealing body from turning inthe tube, the control rod and the threaded bore of this body are set outalong an axle which is off centre in relation to the axle of the tube.

In a particularly advantageous embodiment, the gas distributor tube isequipped with two sliding sealing bodies and with a lateral gas inletsituated between these two bodies. Preferably, the control rod comprisestwo elements threaded in opposite directions and fitted respectivelyinto the two sealing bodies, so as to make these two bodies slidesimultaneously in opposite directions. The control rod can be connectedto the means of control by a coupling which can be disconnected.

BRIEF DESCRIPTION THE DRAWINGS

The present invention can be better understood with the help of thefollowing description of an example of embodiment, with reference to theannexed drawings in which:

FIG. 1 is a schematic lateral elevation view, partly cut, of anembodiment of a gas-burner according to the invention.

FIG. 2 is a schematic cross section view of this burner, along lineII--II of FIG. 1.

FIG. 3 is a longitudinal section view, along line III--III of FIG. 4, ofthe gas distributor tube of this burner and of the adjustment mechanismit contains.

FIG. 4 is a cross section view along line IV--IV of FIG. 3, and

FIG. 5 is an analogous view to FIG. 4 and shows another embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the figures, the linear burner shown comprises anoutside air distributor tube 1, a gas distributor tube 2 fitted insidetube 1 in an adjustable position thanks to a pair of threaded rods 3screwed into the wall of tube 2 and equipped with locknuts 4, and a rowof gas injectors 5 fixed onto tube 2 at right angles to the latter andextending towards the outside, each one through an air injector 6 formedby a tubular opening fixed in an aperture 7 of tube 1. Each air injectorcontains a turbulence ring 8, which favours the mixing of the gas andthe combustion air at the outlet of gas injector 5. This type ofinjector is well known and it is described in more detail in EP-A-0 190091. In the present case, each gas injector 5 is equipped with athreaded collar 9 which is screwed into a tapped bore 10 of the gasdistributor tube 2.

Injectors 5 and 6 are set out in a row and all emerge into a combustionzone 11 defined by a flame guide 12 in refractory steel, which is fixedon the outside of tube 1 by bolting in slides (not shown), these samebeing bolted onto tube 1. The flame guide 12 carries an electric igniter16 and a flame control device 17, for example by detection ofultraviolet radiation. The above-mentioned arrangements are well knownin the field of gas and blown air burners.

In this preferred embodiment example, the gas distributor tube 2 is acylindrical, rectilinear tube, with a longitudinal axis 20 set outapproximately but not necessarily in the centre of tube 1. In the middleof its length, tube 2 is equipped with a lateral gas inlet nozzle 21connected to a supply pipe 22 which goes through the wall of tube 1 andwhich supplies the burner with gas coming, as indicated by arrow G, froman adjustment valve which is not shown. This valve permits the gas flow,and thus the power of the burner, to be adjusted. The gas can be, forexample, natural gas, liquified petroleum gas or a manufactured gas suchas town gas or blast furnace gas. By the inside of tube 2, it reachesthe different injectors 5 fitted in the apertures 10.

One extremity 24 of the air distributor tube 1 is connected to an airsupply pipe 25, by an assembly of flanges 26 equipped with a diaphragm26a controlling the flow of air, which is blown at a low pressure andarrives as indicated by arrow A, then goes around the gas distributortube 2 to reach the air injectors 6 which mix it with the gas at theinlet of the combustion zone 11. The other extremity 27 of tube 1 issealed by a cover 28 fixed onto a flange 29 of the tube and throughwhich runs a control shaft 30 equipped with a manual wheel 31 or with anautomatic control.

The gas distributor tube 2 is shown in more detail in FIGS. 3 and 4. Itis a cylindrical rectilinear tube made of steel, supported by thethreaded rods 3 and holding the gas injectors 5. In order to simplify,only five gas injectors 5a to 5e have been shown. Each end of tube 2 isclosed by a plate 32, 33 fixed by a threaded cap 34, screwed onto theoutside of tube 2.

Two sealing nuts 36, 37 are fitted in a sliding way in the inside boreof tube 2 and each of them closes this bore in an airtight way betweenthe corresponding extremity of the tube and the gas inlet nozzle 21.Each of these nuts can be formed for example by a bronze cylindricalpart pierced with an eccentric longitudinal bore equipped with athreading 38, 39 and centred on an axis 40 which is removed by adistance E compared with axis 20 of tube 2 and of the outside surface ofthe nut. In this example, this gap E is lateral, but it could beforeseen in another direction. A rotary rod 41, * extends longitudinallyin tube 2 and is held by stuffing-box bearings 42, 43 fitted in plates32 and 33. One extremity 44 of the rod 41 goes through the cap 35 and isconnected to the control shaft 30 by means of an appropriate coupling 45(FIG. 1), for example a fork coupling. Inside tube 2, the rotary rod 41is subdivided into two symmetrical elements 48 and 49 made integral inrotation by a coupling-box 50 and elastic pins 51, approximately in themiddle of the length of tube 2. In this zone, each element 48,49 has acylindrical section 52, 53 supported in a rotary way by a respectivebrace 54, 55 fixed in tube 2 by screws 56. On the side of the middle ofthe tube, the element 48,49 is held longitudinally by an elastic ring ofthe "circlips" type 57. On the other side of the brace, it is of greaterdiameter and is equipped with a threading 58, 59 fitted into thethreading 38, 39 of the corresponding nut 36, 37. The threadings 39 and59 are in the normal direction, whereas the threadings 38 and 58 are inthe opposite direction. Each brace 54, 55 is pierced with several holes60, 61 to allow the gas to go along tube 2.

Thus, when the control wheel 31 is turned so as to turn the rod 41 inthe direction of arrow F, i.e. in an anticlockwise direction, the twonuts 36 and 37 cannot turn due to the fact that the rod 41 is maintainedby its bearings in an eccentric position, and slide in the tube, movingsymmetrically closer to one another, whereas they move away from eachother if the rod 41 is turned in the opposite direction. In movingcloser together, the nuts 36 and 37 will seal the apertures 10 in whichare fitted the two injectors 5a and 5e situated at the extremity of therow. The linear flame of the burner will be shortened symmetrically by ashort distance at its two extremities, each time the nuts 36, 37 blockthe supply of a further pair of injectors 5. In the same way, the flamewill become wider if the wheel 31 and the rod 41 are turned in theopposite way. Of course, the adjustment of the gas supply flow at thesame time can be foreseen. This adjustment can be carried outautomatically with a pressure captor on the supply pipe 22. In anotherembodiment, it can be linked to a motorized control of the flame widthadjustment mechanism, activating the rotary rod 41. Meanwhile, the aircontinues to be delivered into the combustion zone 11 by all theinjectors 6, even where the injectors 5 no longer receive any gas. In adrying drum as mentioned above, this has the advantage of helping tocool the zones at the extremities of the drum.

The present invention is not limited to the embodiment described aboveas an example, but can be extended to all modifications or variantsobvious for an expert. In particular, the eccentric layout of rod 41 isnot indispensable, as shown by FIG. 5. In this variant, the nuts 36, 37are replaced by nuts 66, 67 which have a threaded bore centred on theaxle 20 of tube 2. In order to be prevented from turning, each nut isequipped with a lateral groove 68, which slides on a correspondinglongitudinal key 69, fixed in tube 2 by screws 70 and extending over thewhole length of the stroke of the nut. This layout means that one can dowithout the braces 54, 55 of the previous example and use a rod 41 inone single piece. However, the eccentric layout has the advantage offacilitating the airtightness and the manufacturing. In another variant,each nut 36, 37 or 66, 67 could be conceived in two elements, one ofwhich ensures the airtightness and the other serves as a nut proper onthe threading of rod 41.

It must also be noted that the sealing bodies constituted by the nuts36, 37 could be replaced by bodies controlled in a different way, forexample by means of sliding rods controlled from the outside of theburner by a linear activator.

I claim:
 1. A linear gas and air burner comprising an air distributortube (1) connected to a pressurized air supply (A), a gas distributortube (2) located inside the air distributor tube and equipped with a gasinlet (21) connected to a pressurized gas supply (G), and at least onelongitudinal row of gas injectors (5) extending radially from the gasdistributor tube through air injectors (6) connected with air outletapertures made in the wall of the air distributor tube, each gasinjector (5) being connected to a gas outlet aperture (10) made in thewall of the gas distributor tube, wherein the gas distributor tube (2)is inwardly sealed by at least one sliding sealing body (36, 37, 66, 67)positionable so as to block the supply of gas to a desired section ofthe gas distributor tube, the at least one sliding sealing body iscoupled with a control rod (41) extending longitudinally within the gasdistributor tube and linked to control means (30, 31), for controllingthe position of the at least one sliding sealing body, situated outsideof the gas distributor tube, and all the air injectors (6) arecontinuously supplied with air even when the supply of gas to at leastone of the gas injectors (5) is blocked by the at least one slidingsealing body.
 2. A burner according to claim 1, wherein the control rod(41) is rotatable about an axis (40) and comprises at least one threadedsection (58, 59) which engages a corresponding threaded bore (38, 39) ofthe at least one sliding sealing body (36, 37, 66, 67), and the at leastone sliding sealing body is equipped with means (68, 69) for preventingthe at least one sliding sealing body from rotating within the gasdistributor tube.
 3. A burner according to claim 2, wherein the controlrod (41) is rotatably supported by two elements (32, 33) sealingextremities of the gas distributor tube (2), and the control rod extendsthrough at least one of two elements and is linked to the control means(30, 31).
 4. A burner according to claim 2, wherein the gas distributortube (2) and the at least one sliding sealing body (36, 37) have acircular cross section, and to prevent the at least one sliding sealingbody from turning in the tube, the control rod (41) and the threadedbore (38, 39) extend along an axis (40) which is off center relative toa central axis (20) of the tube.
 5. A burner according to claim 2,wherein the control rod (41) comprises two elements (48, 49) threaded inopposite directions and each of the two elements (48, 49) respectivelyengage one of the two sliding sealing bodies (36, 37) so as to make thetwo sliding sealing bodies slide simultaneously in opposite directions.6. A burner according to claim 2, wherein the control rod (41) isconnected to the control means (30, 31) by a coupling (45) which isdisconnectable.
 7. A burner according to claim 1, wherein the gasdistributor tube (2) is equipped with two sliding sealing bodies (36,37, 66, 67) and a lateral gas inlet (21) is situated between the twosliding bodies.
 8. A burner according to claim 7, wherein the controlrod (41) comprises two elements (48, 49) threaded in opposite directionsand each of the two elements (48, 49) respectively engage one of the twosliding sealing bodies (36, 37) so as to make the two sliding sealingbodies slide simultaneously in opposite directions.